Microelectronic assembly having thermoelectric elements to cool a die and a method of making the same

ABSTRACT

A microelectronic assembly is provided, having thermoelectric elements formed on a die so as to pump heat away from the die when current flows through the thermoelectric elements. In one embodiment, the thermoelectric elements are integrated between conductive interconnection elements on an active side of the die. In another embodiment, the thermoelectric elements are on a backside of the die and electrically connected to a carrier substrate on a front side of the die. In a further embodiment, the thermoelectric elements are formed on a secondary substrate and transferred to the die.

BACKGROUND OF THE INVENTION

1). Field of the Invention

This invention relates generally to a microelectronic assembly having a microelectronic die, and more specifically to systems that are used to cool a microelectronic die of such an assembly.

2). Discussion of Related Art

As semiconductor devices, such as processors and processing elements, operate at continually higher data rates and higher frequencies, they generally consume greater current and produce more heat. It is desirable to maintain operation of these devices within certain temperature ranges for reliability reasons, among others. Conventional heat transfer mechanisms have restricted the operation of such devices to lower power levels, lower data rates, and/or lower operating frequencies. Conventional heat transfer mechanisms have limited heat transfer capability due to size and location restrictions, as well as thermal limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by way of examples with reference to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional side view of a portion of a wafer substrate which is partially processed to manufacture a microelectronic assembly, according to an embodiment of the invention;

FIG. 2 is a view similar to FIG. 1, after an opening is etched in a dielectric layer of the partially processed wafer substrate and one thermoelectric element is formed in the opening;

FIG. 3 is a view similar to FIG. 1, after another thermoelectric element, having an opposite doping conductivity type and the thermoelectric element that is formed in FIG. 2, is formed, as well as other components above an integrated circuit of the partially processed wafer;

FIG. 4 is a view similar to FIG. 3, after the wafer is finally processed, singulated into individual dies, and one die is flipped onto a carrier substrate and mounted to the carrier substrate to finalize the manufacture of a microelectronic assembly according to an embodiment of the invention;

FIG. 5 is a side view representing a microelectronic assembly according to another embodiment of the invention having thermoelectric components on a side opposing an active side of a singulated die, and wirebonded to a package substrate on an active side of the die;

FIG. 6 is a side view representing a microelectronic assembly according to a further embodiment of the invention, which defers from the embodiment of FIG. 5 in that short plugs electrically connect thermoelectric elements on one side of the die with conductive interconnection elements formed on an opposing, active side of the die;

FIG. 7 is a side view of two wafer substrates, one carrying active integrated circuits, and the other one carrying thermoelectric elements, used to manufacture a microelectronic assembly according to a further embodiment of the invention;

FIG. 8 is a view similar to FIG. 7, after the thermoelectric elements are located against and attached to contact pads on the integrated circuit;

FIG. 9 is a view similar to FIG. 8, after the assembly of FIG. 8 is singulated into individual pieces, and an integrated circuit and a heat sink are mounted to one of the pieces;

FIG. 10 is a top plan view illustrating components of an electronic assembly according to a further embodiment of the invention, wherein portions of a thermoelectric module are formed on a die and on a heat spreader, and the thermoelectric module is completed when the heat spreader is placed on the die;

FIG. 11 is a cross-sectional side view illustrating a microelectronic assembly according to a further embodiment of the invention, having a metal layer plated on a backside of a die to spread heat from a hot spot to a thermoelectric module; and

FIG. 12 is a top plan view illustrating relative sizes of hot spots and thermoelectric modules to cool the hot spots.

DETAILED DESCRIPTION OF THE INVENTION

A microelectronic assembly is provided, having thermoelectric elements formed on a die so as to pump heat away from the die when current flows through the thermoelectric elements. In one embodiment, the thermoelectric elements are integrated between conductive interconnection elements on an active side of the die. In another embodiment, the thermoelectric elements are on a backside of the die and electrically connected to a carrier substrate on a front side of the die. In a further embodiment, the thermoelectric elements are formed on a secondary substrate and transferred to the die.

FIG. 1 of the accompanying drawings illustrates a portion of wafer 10 which is partially processed to manufacture a microelectronic assembly, according to an embodiment of the invention. The wafer 10 includes a wafer substrate 12, an integrated circuit 14, and a dielectric material 16.

The wafer substrate 10 is typically made of silicon or another semiconductor material. The integrated circuit 14 includes integrated circuit elements 18 that are formed in and on the wafer substrate 12. The integrated circuit elements 18 include transistors, capacitors, diodes, etc. The integrated circuit 14 further includes a plurality of alternating dielectric layers and metal layers. The metal layers include a power plane 20 and a ground plane 22. The integrated circuit 14 further includes contact pads 24, including a power contact 24P, a ground contact 24G, and a signal contact 24I.

Further, plugs, vias, and metal lines in the dielectric layers of the integrated circuit 14 form electric links 26, only a few of the electric links 26 being shown.

The electric links 26 include a power electric link 26P1 interconnecting the power contact pad 24P with the power plane 7, and a power electric link 26P2 interconnecting the power plane 20 with the integrated circuit elements 18. As such, power can be provided through the power contact pad 24P, the power electric link 26P1, the power plane 7, and the power electric link 26P2 to one or more of the integrated circuit elements 18.

The electric links 26 include a ground electric link 26G1 interconnecting the ground contact pad 24G with the ground plane 22, and a ground electric link 26G2 interconnecting the ground plane 22 with the integrated circuit elements 18. As such, ground can be provided through the ground contact pad 24G, the ground electric link 26G1, the ground plane 22, and the ground electric link 26G2 to one or more of the integrated circuit elements 18.

A signal electric link 26I interconnects a signal contact pad 24I with one or more of the integrated circuit elements 18, and is disconnected from both the power plane 20 and the ground plane 22. Signals can be provided to and from the integrated circuit elements 18 through more signal electric links such as the signal electric link 26I.

The dielectric material 16 is formed in a layer over the integrated circuit 14. The dielectric material 16 initially covers the contact pads 24. A first opening 28 is then etched in the dielectric material 16, which exposes an area of the power contact pad 24P.

As illustrated in FIG. 2, an thermoelectric element 30 is subsequently formed in the opening 28 of FIG. 1. Layers of the thermoelectric element 30 may be electrolessly plated or sputtered, and include a diffusion barrier layer 32, a p-doped semiconductor material 34 such as p-doped Bi₂Te₃, alloys of Bi₂Te₃ and Sb₂Te₃, or alloys of Si and Ge, and a diffusion barrier layer 36, formed sequentially on top of one another.

As illustrated in FIG. 3, another thermoelectric element 40 is formed adjacent to the thermoelectric element 30 on the power contact pad 24P. The thermoelectric element 40 is formed in an opening that is formed in the dielectric material 16 after the thermoelectric element 30 is formed. In order to form the opening for the thermoelectric element 40, a photoresist layer is formed over the dielectric material 16, and an opening is masked in the photoresist layer above where the thermoelectric element 40 is to be formed. Using the photoresist layer as a mask, the opening where the thermoelectric element 40 is to be formed is then etched in the dielectric material 16. The thermoelectric element 40 includes a diffusion barrier layer 42, an n-doped semiconductor material 44 such as n-doped Sb₂Te₃, alloys of Bi₂Te₃ and Sb₂Te₃, or alloys of Si and Ge, and a diffusion barrier layer 46 formed sequentially on top of one another. The thermoelectric element 40 is thus the same as the thermoelectric element 30, except that the semiconductor material 34 is p-doped, whereas the semiconductor material 44 is n-doped.

Conductive spacer components 48 and 50 are subsequently formed on the ground and signal contact pads 24G and 24I, respectively. Openings in which the conductive spacer components 48 and 50 are formed may be etched by forming a photoresist layer over the dielectric material 16 and the thermoelectric elements 30 and 40, masking the photoresist layer, and then using openings in the masked photoresist layer to etch the openings where the conductive spacer components 48 and 50 are to be formed in the dielectric material 16. The conductive spacer components 48 and 50 are typically made of a metal.

Conductive interconnection elements 54 are subsequently formed, each on a respective one of the thermoelectric elements 30 or 40, or the conductive spacer components 48 or 50. The conductive interconnection elements 54 stand proud of the dielectric material 16 so as to have upper surfaces 56 that are in a common plane above an upper plane of the dielectric material 16.

Only a portion of the wafer 10 is illustrated in FIGS. 1 to 3. It should, however, be understood that the wafer includes a plurality of the integrated circuits 14 that are formed in rows and columns extending in x- and y-directions across the wafer, each having an identical layout of thermoelectric elements 30 and 40, conductive spacer components 48 and 50, and conductive interconnection elements 54.

The wafer 10 is subsequently diced or singulated into individual dies, each die carrying a respective integrated circuit and related connections. Each die will include components represented in the portion of the wafer 10 illustrated in FIG. 3.

FIG. 4 illustrates one such die 10A, which is flipped and located on a carrier substrate in the form of a package substrate 60. Package terminals 62 are formed on an upper surface of the package substrate 60. Each one of the conductive interconnection elements 54 is in contact with a respective package terminal 62.

The entire microelectronic assembly 70, including the die 10A and the package substrate 60, is then inserted in a furnace to reflow the conductive interconnection elements 54. The conductive interconnection elements 54 soften and melt, and are subsequently allowed to cool and again solidify. Each conductive interconnection element 54 is then attached to a respective package terminal 62, thereby mounting the die 10A to the package substrate 60 and electrically interconnecting the die 10A and the package substrate 60.

In use, power can be provided through the package substrate 60 through one of the package terminals 62A to the thermoelectric element 30. The current flows toward the die through the n-doped semiconductor material 44. As will be understood in the art of thermoelectrics, current flowing through an n-doped semiconductor material causes heat to be pumped in a direction opposite to the direction that the current flows. As such, heat is pumped in a direction away from the integrated circuit 14 through the thermoelectric element 30 toward the package substrate 60. The current flowing through the thermoelectric element 30 is bifurcated. One portion of the current provides power to some of the integrated circuit elements 18, while some of the current flows through the power contact pad 24P and then through the thermoelectric element 40 to the package terminal 62B. The current flowing through the p-doped semiconductor material 34 causes heat to be pumped in a direction that the current flows. The current flowing through the p-doped semiconductor material 34 flows away from the integrated circuit 14, and thus pumps heat away from the integrated circuit 14.

In another embodiment, the power contact pads providing power to the thermoelectric elements may be separate from power contact pads providing power to the circuit. This will allow separate control over the thermoelectric unit. Such a configuration may be useful where it is necessary to maintain voltage provided to the circuit and not have the voltage be affected by power provided to the thermoelectric module.

It can thus be seen that the p-doped semiconductor material 34 and n-doped semiconductor material 44 both pump heat away from the integrated circuit 14. Localized cooling can thus be provided to the integrated circuit 14. More structures, such as the structure including the thermoelectric elements 30 and 40 may be formed at desired locations across the integrated circuit 14, where additional cooling may be required. What should also be noted is that the same array of package terminals 62 that provide current to the thermoelectric elements 30 and 40 also provide power, ground, and signal to the integrated circuit 14. What should further be noted is that cooling is provided where it is required. When a certain region in an x-y direction of an integrated circuit requires power, the power is provided through thermoelectric elements in the same region. An increase in power requirements in a particular area will correspond with an increase in heat being generated in that particular area. An increase in power in the particular area will also correspond with an increase in current flowing through thermoelectric elements in that particular area. As such, current flowing through thermoelectric elements in a particular area will increase when there is an increase of heat being generated in the particular area.

FIG. 5 illustrates another microelectronic assembly 70, including a carrier substrate in the form of a package substrate 72, a die 74 mounted to the package substrate 72, thermoelectric elements 76 on the die 74, an integrated heat spreader 78, and a heat sink 80. The die 74 is mounted and electrically connected through conductive interconnection elements 82 to the package substrate 72.

The thermoelectric elements 76 are formed in the same manner as the thermoelectric elements 30 and 40 of FIG. 3. Some of the thermoelectric elements 76 have p-doped semiconductor materials, and some have n-doped semiconductor material. The thermoelectric elements 76 are arranged such that, when current flows therethrough, heat is pumped from an upper surface of the die 76 toward the integrated heat spreader 78.

The integrated heat spreader 78 is in direct contact with the thermoelectric elements 76, and the heat sink 80 is located on the integrated heat spreader 78. As will be commonly understood, the heat sink 80 includes a base and plurality of fins extending from the base, from which the heat can be convected to surrounding atmosphere.

Wirebonding wires 84 are provided, through which current can be provided to or be conducted away from the thermoelectric elements 76. Each wirebonding wire 84 has one end connected to a pad on an upper surface of the die 74, the pad being connected to a first of the thermoelectric elements 76. An opposing end of the respective wirebonding wire 84 is bonded to a package terminal on the package substrate 72. The current flows from the package terminal through the respective wirebonding wire 84 and the respective contact through the first thermoelectric element 76. The current can then flow through an even number of the thermoelectric elements 76 and return through another one of the wirebonding wires 84 to the package substrate 72.

FIG. 6 illustrates a microelectronic assembly 86 according to a further embodiment of the invention. The microelectronic assembly 86 is the same as the microelectronic assembly 70 of FIG. 5, and like reference numerals indicate like components. The primary difference is that the microelectronic assembly 86 includes a die 88 which is much thinner than the die 74 of FIG. 5. Short plugs 90 are formed through the die 88. Some of the thermoelectric elements 76 are aligned with respective ones of the plugs 90 and respective ones of the conductive interconnection elements 82. Current can be provided through a respective conductive interconnection element 82 and a respective plug 90 to a respective thermoelectric element 76. The current can then flow through an even number of the thermoelectric elements 76 and return through another one of the plugs 90 and another one of the conductive interconnection elements 82 aligned with one another.

FIGS. 7 through 8 illustrate the manufacture of a microelectronic assembly, wherein thermoelectric elements are manufactured on a separate substrate and then transferred to integrated circuits at wafer level. The combination wafer is then singulated into individual pieces.

Referring specifically to FIG. 7, a wafer 94 is provided, having a wafer substrate 96, integrated circuits 98 formed on the wafer substrate 96, and contact pads 100 formed on the integrated circuits 98. FIG. 7 also illustrates a transfer substrate 102 having thermoelectric elements 104 formed thereon in a manner similar to the thermoelectric elements 30 and 40 of FIG. 3. FIG. 7 also illustrates interconnection structures in the form of spacers 106. The thermoelectric elements 104 and spacers 106 have conductive interconnection elements 108 formed thereon.

As illustrated in FIG. 7, each conductive interconnection element 108 is brought into contact with a respective one of the contact pads 100. The conductive interconnection elements 108 are then attached to the contact pads 100 by a thermal reflow process. A combination wafer 110 is provided that includes the wafer substrates 96 and 102.

Reference is now made to FIG. 9. The combination wafer 110 of FIG. 8 is singulated into separate pieces 112. The wafer 96 is thus separated into pieces 96A and 96B, and the wafer 102 is separated into pieces 102A and 102B. The pieces 112 are identical, and each includes a respective integrated circuit 98. Metallization is provided in an upper level of the pieces 102A and 102B. The pieces may be mounted on supporting substrates and wirebonded to the supporting substrates. Alternatively, the pieces 102A and 102B may be thinned down and through-vias in the pieces 102A and 102B may connect the metallization electrically to the supporting substrates.

An integrated heat spreader 114 can then be mounted to a backside of the wafer substrate portion of a piece 96A, i.e., opposing the integrated circuit 98, and a heat sink 116 can be located and mounted against the integrated heat spreader 114.

FIG. 10 illustrates components of a microelectronic assembly 120 which is partially manufactured according to a further embodiment of the invention. The components of the microelectronic assembly 120 include a die 122, a thermally conductive metal heat spreader 124, a first plurality of conductive copper components 126, a second plurality of conductive copper components 128, and a plurality of thermoelectric elements 130.

The die 122 is as hereinbefore described, for example, with reference to FIG. 5, and is first mounted to a package substrate as described with reference to FIG. 5. A microelectronic circuit is thus formed on a front side of a supporting substrate of the die 122. The first copper components 126 are subsequently formed, e.g., by plating, on a backside of the supporting substrate.

A thin layer of electrically insulating material is formed on a surface of the heat spreader 124. The second plurality of components 128 are formed, e.g., by plating, on the thin layer of electrically insulating material. The thermoelectric elements 130 are subsequently formed on the second plurality of components 128. One p-doped thermoelectric element 130A and one n-doped thermoelectric element 130B is formed on each respective one of the second plurality of components 128.

The heat spreader 124 is flipped so that the thermoelectric elements 130 are an opposing side than shown in FIG. 10. The thermoelectric elements 130 are positioned above the first plurality of components 126. The die 122 and heat spreader 124 are then brought relatively toward one another until the thermoelectric elements 130 contact the first plurality of components 126. The first plurality of components 126 provide missing connections between the thermoelectric elements 130 so that the thermoelectric elements 130, together with the components 126 and 128, are connected in series.

It can thus be seen that a thermoelectric circuit is formed directly on the die 122 and between the die 122 and the heat spreader 124. The thermoelectric elements 130 are manufactured at a high temperature and under processing conditions that may cause damage to the microelectronic circuit of the die 122. However, by manufacturing the thermoelectric elements 130 first on the separate heat spreader 124, and subsequently placing the thermoelectric elements 130 on the die 122, damage to the die 122 can be avoided.

FIG. 11 illustrates a microelectronic assembly 140, according to a further embodiment of the invention, including a package substrate 142, a die 144, a thermally conductive metal heat spreader 145, a copper metal layer 146, a thermoelectric module 148, and a thermal interface material 150.

The die 144 has a microelectronic circuit formed on a front side of a supporting substrate thereof. The die 144 is typically thinned down to a thickness of less than 100 microns. Interconnection elements 151 are formed on a front side of the die 144, and are used to connect the die 144 electrically and structurally to the package substrate 142. The die 144 and package substrate 142 are thus similar to the die 74 and package substrate 72 described with reference to FIG. 5.

The metal layer 146 is plated on a backside of the supporting substrate of the die 144. An opening is made in the metal layer 146, and the thermoelectric module 148 is manufactured within the opening.

In use, the metal layer 146 between the thermoelectric module 148 and the die 144 serves to spread heat from a hot spot created by the microelectronic circuit of the die 144. FIG. 12 illustrates that more than one hot spot 152A and 152B may be formed over an area of the die 144. A respective thermoelectric module 148A and 148B is manufactured over a respective one of the hot spots 152A and 152B. The thermoelectric modules 148A and 148B are relatively large when compared to the hot spots 152A and 152B, so that they can remove a relatively large amount of heat. Notwithstanding the sizes of the thermoelectric modules 148A and 148B, when compared to the hot spots 152A and 152B, outer regions of the thermoelectric modules 148A and 148B can still remove heat from the hot spots 152A and 152B, because heat from the hot spot will spread laterally as it flows through the silicon and the portion of the metal layer (146 in FIG. 11) between the respective thermoelectric module 148A or 148B and the respective hot spot 152A or 152B.

Referring again to FIG. 11, the interface material 150 is subsequently formed over the thermoelectric module 148 and the metal layer 146, and the heat spreader 145 is located against the thermal interface material 150. Heat conducting through the metal layer 146 and being pumped by the thermoelectric module 148 can conduct through the interface material 150 and the heat spreader 145 and be convected to atmosphere.

A power cable 154 is connected to the thermoelectric module 148 to provide power thereto. In the present embodiment, an opening 156 is formed through the heat spreader 145, and the cable 154 extends through the opening 156. Additionally, a heat sink (not shown) with fins can be placed upon the heat spreader 145.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art. 

1. A method of making a microelectronic assembly comprising: forming a metal layer directly on a semiconductor material of a first side of a die having first and second sides wherein the first side of the die is provided on a supporting substrate and the die having a microelectric circuit formed on the second side of the die; forming an opening in the metal layer; forming a thermoelectric module in the opening of the metal layer, the metal layer between the thermoelectric module and the die; locating a heat spreader that is thermally coupled to the thermoelectric module; forming an opening through the heat spreader; and locating a base of a heat sink having fins extending from the base and the base is thermally coupled to the thermoelectric module.
 2. The method of claim 1, wherein the metal layer is plated.
 3. The method of claim 1, wherein the metal layer includes copper.
 4. The method of claim 1, wherein the thermoelectric module is formed over a first area only of the supporting substrate, to allow for selective cooling of the first area as opposed to a second area of the supporting substrate.
 5. The method of claim 4, wherein the microelectronic circuit, when operated, creates a hot spot within the first area.
 6. The method of claim 5, wherein the metal layer spreads heat from the hot spot to the thermoelectric module.
 7. A microelectronic assembly, comprising: a supporting substrate of semiconductor material; a microelectronic circuit formed directly on the semiconductor material of the supporting substrate; a metal layer formed directly on the semiconductor material of the supporting substrate and on a side of the supporting substrate opposing the microelectronic circuit, the metal layer having an opening; a thermoelectric module in the opening of the metal layer, the metal layer between a first side of the thermoelectric module and the support substrate; and a metal heat spreader formed over a second side of the thermoelectric module, the second side opposite the first side, wherein the metal heat spreader has an opening.
 8. The microelectronic assembly of claim 7, wherein the metal layer includes copper.
 9. The microelectronic assembly of claim 7, wherein the thermoelectric module is formed over a first area only of the supporting substrate to allow for selective cooling of the first area opposed to a second area of the supporting substrate.
 10. The microelectronic assembly of claim 9, wherein the microelectronic circuit, when operated, creates a hot spot within the first area.
 11. The method of claim 10, wherein the metal layer spreads heat from the hot spot to the thermoelectric module. 